1. Field of the Invention
The present invention relates to acoustic processing technology, and more particularly to a three-dimensional acoustic processor which provides a three-dimensional acoustic effect to a listener in a reproducing sound field via a headphone or the like.
2. Description of Related Art
In general, to achieve accurate reproduction or location of a sound image, it is necessary to obtain the acoustic characteristics of the original sound field up to the listener and the acoustic characteristics of the reproducing sound field from the acoustic output device, such as a speaker or a headphone, to the listener. In an actual reproducing sound field, the former acoustic characteristics are added to the sound source and the latter characteristics are removed from the sound source, so that even using a speaker or a headphone it is possible to reproduce to the listener the sound image of the original sound image of the original sound field, or so that it is possible to accurately localize the position of the original sound image.
In the past, in order to add the acoustic characteristics from the sound source to the listener of the original sound field and remove the acoustic characteristics of the reproducing sound field from the acoustic output device such as a speaker or a headphone up to the listener, a FIR (finite impulse response, non-recursive) filter having coefficients that are the impulse responses of each of the acoustic spatial paths was used as a filter to emulate the transfer characteristics of the acoustic spatial path and the reverse of the acoustic characteristics of the reproducing sound field up to the listener.
However, when measuring the impulse response in a normal room for the purpose of obtaining the coefficients of an FIR filter in the past, the number of taps of the FIR which represent those characteristics when using an audio-signal sampling frequency of 44.1 kHz is several thousand or even greater. Even in the case of the inverse of the transfer characteristics of a headphone, the number of taps required is several hundred or even greater.
Therefore, when using FIR filters, there is a huge number of taps and computation required, causing the problems that in an actual circuit implementation it is necessary to have a plurality of parallel DSPs or convolution processors, this hindering a reduction in cost and the achievement of a physically compact circuit.
In addition, in the case of localizing the sound image, it is necessary to perform parallel processing of a plurality of channel filters for each of the sound image positions, making it even more difficult to solve the above-noted problems.
Additionally, in an image-processing apparatus which processes images which have accompanying sound images, such as in real-time computer graphics, the amount of image processing is extremely great, so that if the capacity of the image-processing apparatus is small or many images must be processed simultaneously, the insufficient processing capacity produces cases in which it is not possible to display a continuous image, and the image appears as a jump-frame image. In such cases, there is the problem that the movement of the sound image, which is synchronized to the movement of the visual image, becomes discontinuous. In addition, in cases in which the environment is different from the expected visual/auditory environment of, for example, the user's position, there is the problem of the apparent movement of the visual image being different from the movement of the sound image.